phrase 'atheism is the null hypothesis' before, but I've decided to give it a brief revisit.
The null hypothesis is a term used in science to help weed out parts of theories that can be shaved by Ockam's Razor. When performing a scientific test, the null hypothesis refers to a specific variable that you can assume is not necessary to the success of the test. If it was removed, the test would work as well as it does when it is present. So when it comes to describing the test and its method, you needn't even mention the variable, because it has no effect whatsoever.
This is how atheists feel about the universe and God. They see atheism as the null hypothesis, with God as the useless variable, because they see that the universe runs just fine without him.
But isn't that quite clearly concluding atheism based on the presupposition of atheism? Yes. Yes it is.
Theologies tend to have God in a position that he not only created the universe, but he maintains and sustains it. He's always up to something. So whatever scientific test is done on the universe, is always going to give a result in line with what God is doing (if he is there.. which he is).
So by doing science, an atheist simply can't know if atheism is the null hypothesis. If God exists, the universe will work as it does. If God does not exist, the universe will work as it does.
You can't take a scientific result and say we don't need God for this to work. God is not a measurable quantity, so you don't know how much of him is in the test.
It could be pulled some way in the atheists favour like this though (but not much). When Napoleon asked Laplace where God fit into his mathematical work, the scientist answered "Sir, I have no need of that hypothesis."
Maybe it is the case that certain systems don't need God to function. They're working mechanically with all the parts and information they need to get along with. God doesn't need to crank a handle and turn cogs. But as John Lennox likes to ask, "What is the explanation for the motor car? The combustion engine or Henry Ford?"
Just because you have the function, the mechanism, and it's all good to go without any further input from a creator, it doesn't mean there wasn't a creator. They're a different kind of explanation, and any designed system needs both.
So to say atheism is the null hypothesis, is a completely baseless assertion. Instead, any tests about systems in the universe need to be a process of elimination, finding which ones function without God, or can only function with him. As it goes, some things need him regularly, others are on autopilot.
Atheists can have hope and faith that one day, the universe will be proven to exist and function without God, but at the moment, they aren't there, and it's dishonest to pretend otherwise.